The goal of the proposed research is to understand the role of intracellular proteases and peptidases in bacterial physiology. This problem will be approached using a combination of genetic and biochemical methods. Mutants of Salmonella typhimurium lacking six different peptidases and three endoproteases have already been obtained. Strains carrying some of these mutations are deficient in protein turnover and also accumulate small peptides during growth. Mutations affecting other peptidases and proteases will be sought in Salmonella and when appropriate in Escherichia coli and the effects of all of these mutations on degradation of nonfunctional proteins, protein turnover during starvation, protein modification and maturation, protein secretion, and other cell processes likely to involve proteolysis will be studied. The properties of these mutants should allow individual proteases to be assigned a role in particular physiological processes. Proteases shown to be involved in important processes will be purified and characterized biochemically in order to understand in detail the pathways in which they act.